SALMONELLA AND E. COLI O157:H7 PREVALENCE IN CATTLE AND ON CARCASSES IN A VERTICALLY INTEGRATED FEEDLOT AND HARVEST PLANT IN MEXICO

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Microbial contamination can create serious health risks and trade problems in the international food trade, this is essential for the economy of many countries. In Mexico scientific information regarding Salmonella and E. coli O157:H7 prevalence at pre and post-harvest in Mexico is scarce. Therefore, this research has three general objectives: i) to determine the prevalence of Salmonella and E. coli O157:H7 in a Mexican cattle feedlots and its impact for subsequent contamination on carcasses, ii) to determine if there is a seasonal effect on the prevalence of E. coli O157:H7 at feed lot levels and iii) to compare the prevalence of Salmonella and E. coli O157:H7 on carcasses destined for different markets and processed under TIF certification in Mexico. Two-hundred-fifty animals were randomly selected and composite samples were taken from three anatomical carcass sites (inside round, hind shank and fore shank). Samples were taken from the hides, intestinal feces (IF), at pre-evisceration (PE), pre-cooler (PC) and after 24 hours of dry chilling (DC) in the coolers. Additionally, 250 samples from fecal (FL) and water samples were taken from the lairage area. E. coli O157:H7 and Salmonella detection was carried out using BAX (PCR), IMS and conventional methods. Logistic regression models were used to determine areas of highest risk. A total of 1,695 samples were collected from different locations of the integration, feedlot and harvesting slaughter plant. Salmonella was isolated from 52.5% of these samples. The highest prevalence was found in hides (92.4%), followed by feces from the holding pens (HP) (91.0%), feces from feedlots (FL) (55.56%), pre-evisceration (PE) (49.0%), intestinal feces (IF) (46.8%) and pre-cooler (PC) (24.8%) for all sampling periods combined. The lowest prevalence was found in the carcasses after 24 hours of DC in the cooler (6.0%). The overall prevalence of E. coli O157 was as follows: hides 11.7%, intestinal feces 5.2%, feedlots 2.7%, holding pens 2.0%, pre-evisceration 0.8%, pre-cooler 0.4% and cooler 0.4%. E. coli O157:H7 was recovered mainly in the summer, 6.8% (43/632), followed by winter 1.79% (12/670), however in spring all the samples at the feedlot and at the slaughter plant tested negative. Salmonella was recovered in all seasons with significant variations (P < 0.0001), the percentages being as follows: spring 59.7% (200/235), summer 53.64% (339/632) and winter 44.2% (297/672). An effect due to seasonality on Salmonella and E. coli O157:H7 was not clear. The prevalence of the carcasses destined for different markets did not show differences (P>0.05) for Salmonella and/or E. coli O157:H7 prevalence (P > 0.05). These results are an alert as to the risks of contamination in meats for these pathogens, show the necessity of implementing programs for food safety and microbiological interventions, and demonstrate the need for further research.